Process for thinning a semiconductor workpiece

ABSTRACT

The present invention provides an apparatus and method for use in processing semiconductor workpieces. The new apparatus and method allows for the production of thinner workpieces that at the same time remain strong. Particularly, a chuck is provided that includes a body, a retainer removeably attached to the body and a seal forming member. When a workpiece is placed on the chuck body and the retainer is engaged to the body, a peripheral portion of the back side of the workpiece is covered by the retainer while an interior region of the back side of the workpiece is exposed. The exposed back side of the workpiece is then subjected to a wet chemical etching process to thin the workpiece and form a relatively thick rim comprised of semiconductor material at the periphery of the workpiece. The thick rim or hoop imparts strength to the otherwise fragile, thinned semiconductor workpiece. Semiconductor workpieces made according to the present invention offer an improved structure for handling thinned wafers in conventional automated equipment. This results in improved yields and improved process efficiency.

TECHNICAL FIELD

The invention relates to a process and apparatus for use withworkpieces, such as semiconductor wafers, flat panel displays, rigiddisk or optical media, thin film heads or other workpieces formed from asubstrate on which microelectronic circuits, data storage elements orlayers, or micro-mechanical elements may be formed. These and similararticles are collectively referred to herein as a “wafer” or“workpiece.” Specifically, the present invention relates to a processand apparatus for use in thinning semiconductor workpieces.

BACKGROUND OF THE INVENTION

State of the art electronics (e.g., cellular phones, personal digitalassistants, and smart cards) demand thinner integrated circuit devices(“ICD”). In addition, advanced packaging of semiconductor devices (e.g.,stacked dies or “flip-chips”) provide dimensional packaging constraintswhich also require an ultra-thin die. Moreover, as operating speeds ofICDs continue to increase heat dissipation becomes increasinglyimportant. This is in large part due to the fact that ICDs operated atextremely high speeds tend to generate large amounts of heat. That heatmust be removed from the ICD to prevent device failure due to heatstress and to prevent degradation of the frequency response due to adecrease in carrier mobility. One way to enhance thermal transfer awayfrom the ICD, thereby mitigating any deleterious temperature effects, isby thinning the semiconductor wafer from which the ICD is fabricated.Other reasons for thinning the semiconductor wafer include: optimizationof signal transmission characteristics; formation of via holes in thedie; and minimization of the effects of thermal coefficient of expansionbetween an individual semiconductor device and a package.

Semiconductor wafer thinning techniques have been developed in responseto this ever increasing demand for smaller, higher performance ICDs.Typically, semiconductor devices are thinned while the devices are inwafer form. Wafer thicknesses vary depending on the size of the wafer.For example, the thickness of a 150 mm diameter silicon semiconductorwafer is approximately 650 microns, while wafers having a diameter of200 or 300 mm are approximately 725 microns thick. Mechanical grindingof the back side of a semiconductor is one standard method of thinningwafers. Such thinning is referred to as “back grinding.” Generally, theback grinding process employs methods to protect the front side ordevice side of the semiconductor wafer. Conventional methods ofprotection of the device side of the semiconductor wafer includeapplication of a protective tape or a photoresist layer to the deviceside of the wafer. The back side of the wafer is then ground until thewafer reaches a desired thickness.

However, conventional back grinding processes have drawbacks. Mechanicalgrinding induces stress in the surface and edge of the wafer, includingmicro-cracks and edge chipping. This induced wafer stress can lead toperformance degradation and wafer breakage resulting in low yield. Inaddition, there is a limit to how much a semiconductor wafer can bethinned using a back grinding process. For example, semiconductor wafershaving a standard thickness (as mentioned above) can generally bethinned to a range of approximately 250-150 microns.

Accordingly, it is common to apply a wet chemical etch process to asemiconductor wafer after it has been thinned by back grinding. Thisprocess is commonly referred to as stress relief etching, chemicalthinning, chemical etching, or chemical polishing. The aforementionedprocess relieves the induced stress in the wafer, removes grind marksfrom the back side of the wafer and results in a relatively uniformwafer thickness. Additionally, chemical etching after back grindingthins the semiconductor wafer beyond conventional back grindingcapabilities. For example, utilizing a wet chemical etch process afterback grinding allows standard 200 and 300 mm semiconductor wafers to bethinned to 100 microns or less. Wet chemical etching typically includesexposing the back side of the wafer to an oxidizing/reducing agent(e.g., HF, HNO₃, H₃PO₄, H₂SO₄) or alternatively to a caustic solution(e.g., KOH, NaOH, H₂O₂). Examples of wet chemical etching processes maybe found in co-pending U.S. patent application Ser. No. 10/631,376,filed on Jul. 30, 2003, and assigned to the assignee of the presentinvention. The teachings of application Ser. No. 10/631,376 areincorporated herein by reference.

Although methods for thinning semiconductor wafers are known, they arenot without limitations. For example, mounting a semiconductor wafer toa submount or “chuck” (as it is commonly known) so that the wafer can bethinned requires expensive coating and bonding equipment and materials,increased processing time, and the potential for introducingcontaminates into the process area. Additionally, adhesives for bondinga wafer to a chuck that may be useful in a mechanical grinding processwill not withstand the chemical process fluids used in wet chemicaletching. Furthermore, the current use of a photoresist or adhesive tapefails to provide mechanical support for very thin wafers either duringthe back grind process or in subsequent handling and processing. The useof tape also creates obstacles in the removal process. For example, taperemoval may subject a wafer to unwanted bending stresses. In the case ofa photoresist, the material is washed off the device side of a waferwith a solvent, adding to the processing time and use of chemicals, andincreasing the risk of contamination. The use of taping and protectivepolymers are also costly, since both equipment and materials arenecessary to apply and remove the protective media.

Further, thinned semiconductor wafers are prone to warping and bowing.And because thinned semiconductor wafers can be extremely brittle, theyare also prone to breakage when handled during further processing.Thinned semiconductor wafers (e.g., below 250 microns) also presentcomplications in automated wafer handling because, in general, existinghandling equipment has been designed to accommodate standard waferthicknesses (e.g., 650 microns for 150 mm wafer and 725 microns for 200and 300 mm wafers).

Accordingly there is a need for a process and equipment for producingthinner semiconductor workpieces. At the same time, there is a need toprovide thinner workpieces that are strong enough to minimize the riskof breakage, yet remain compatible with conventional automatedsemiconductor wafer handling equipment. Finally, it would beadvantageous to develop a system that reduces the number of processingsteps for thinning a semiconductor workpiece.

SUMMARY OF THE INVENTION

The present invention provides a method and apparatus for use inprocessing semiconductor wafers. The new system and apparatus allows forthe production of thinner wafers that at the same time remain strong andresistant to bowing and warping. As a result, the wafers produced by thepresent process are less susceptible to breakage. The process andequipment of the present invention also offers an improved productstructure for handling thinned wafers, while reducing the number ofprocessing steps. This results in, among other things, improved yieldsand improved process efficiency.

In one aspect, the present invention provides a chuck for receiving andsupporting a semiconductor workpiece having a device side, a bevel and aback side. The chuck has a body for supporting the workpiece, a retainerremoveably attached to the body and adapted to cover a peripheralportion of the back side of the workpiece, and at least one member forcreating a seal between the retainer and the back side of the workpiece.Due to its configuration, the chuck permits an interior region of theback side of the workpiece to be exposed, while protecting theperipheral portion of the back side of the workpiece. The workpiece isthen thinned via a wet etching process. The result is a processedsemiconductor workpiece that has a thinned main body (e.g., less thanapproximately 125 microns) and a thick rim (e.g., in a range ofapproximately 600 to 725 microns). The relatively thicker rim providesstrength to the thinned workpiece and permits the workpiece to behandled for additional processing with conventional automated handlingequipment.

In another aspect, the present invention provides a semiconductorworkpiece having a main body and a rim comprised of semiconductormaterial. The main body is integrally connected to the rim and has athickness less than approximately 50% of the rim thickness. Therelatively thick rim provides strength to the workpiece, preventing themain body from bowing and warping. Meanwhile, the main body of thesemiconductor workpiece can be thinned to a thickness less than 300microns, preferably less than 125 microns, more preferably less than 100microns, especially less than 50 microns and even less than 25 microns.The structural configuration of thinned semiconductor workpieces of thepresent invention meet the industry demand for thinned ICDs necessary intoday's state of the art electronics and advanced packaging techniques,while at the same time, reducing the risk of breakage due to the fragilestate of the thinned workpiece.

The present invention also provides several processes for thinning asemiconductor workpiece. In one aspect, the process includes the stepsof placing the semiconductor workpiece into a chuck adapted to cover aperipheral portion of the back side of the workpiece, leavingapproximately 95% of the back side surface of the workpiece exposed. Thesemiconductor workpiece is then thinned via a wet chemical etchingprocess wherein the back side of the workpiece is exposed to anoxidizing agent (e.g., HF, HNO₃, H₃PO₄, H₂SO₄) or alternatively to acaustic solution (e.g., KOH, NaOH, H₂O₂). During the wet chemicaletching step, the exposed back side of the workpiece is thinned to athickness less than 50% of the pre-wet chemical etching thickness of theworkpiece. As a result, a rim is formed at the periphery of theworkpiece, or as it is commonly referred to in the industry, the“exclusion zone.” The rim has a thickness approximately equal to thethickness of the workpiece prior to the wet chemical etch step (e.g., ina range of 600 to 725 microns). The remainder of the workpiece (i.e.,the thinned main body) has a thickness less than 50% of the rimthickness (e.g., less than 300 microns, preferably less than 125microns, more preferably less than 100 microns, especially less than 50microns and even less than 25 microns). This process eliminates thelimitations associated with known methods of thinning semiconductorworkpieces mentioned above, while increasing overall manufacturingefficiencies.

Any of the described aspects of the invention may be combined and/orrepeated one or more times to achieve optimal results. The inventionresides as well in sub-combinations of the aspects described. These andother objects, features and advantages of this invention are evidentfrom the following description of preferred embodiments of thisinvention, with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a perspective view of a chuck according to the presentinvention with a semiconductor workpiece secured therein prior tothinning.

FIG. 1B is a cross-sectional view of the chuck and workpiece shown inFIG. 1A.

FIG. 1C is a partial enlarged view of the chuck and workpiece shown inFIG. 1B, demonstrating the cooperation between the chuck and theworkpiece.

FIG. 1D is an exploded cross-sectional view of the chuck and workpieceshown in FIG. 1A.

FIG. 1E is a partial enlarged view of the chuck and workpiece sectionidentified as X shown in FIG. 1D.

FIG. 2A is a cross-sectional view of another embodiment of a chuckaccording to the present invention with a workpiece secured thereinprior to thinning.

FIG. 2B is a partial enlarged view of the chuck and workpiece shown inFIG. 2A, demonstrating the cooperation between the chuck and theworkpiece.

FIG. 3A is a cross-sectional view of yet another embodiment of a chuckaccording to the present invention with a workpiece secured thereinprior to thinning.

FIG. 3B is a partial enlarged view of the chuck and workpiece shown inFIG. 3A, demonstrating the cooperation between the chuck and theworkpiece.

FIG. 4A is a cross-sectional view of another embodiment of a chuckaccording to the present invention with a workpiece secured thereinprior to thinning.

FIG. 4B is a partial enlarged view of the chuck and workpiece shown inFIG. 4B, demonstrating the cooperation between the chuck and theworkpiece.

FIG. 5A is a cross-sectional view of another embodiment of a chuckaccording to the present invention with a workpiece secured thereinprior to thinning.

FIG. 5B is a partial enlarged view of the chuck and workpiece shown inFIG. 5A, demonstrating the cooperation between the chuck and theworkpiece.

FIG. 6A is a cross-sectional view of yet another embodiment of a chuckaccording to the present invention with a workpiece secured thereinprior to thinning.

FIG. 6B is a partial enlarged view of the chuck and workpiece shown inFIG. 6A, demonstrating the cooperation between the chuck and theworkpiece.

FIG. 7A is a cross-sectional view of an embodiment of a chuck accordingto the present invention with a workpiece secured therein prior tothinning.

FIG. 7B is a partial enlarged view of the chuck and workpiece shown inFIG. 7A, demonstrating the cooperation between the chuck and theworkpiece.

FIGS. 8 and 9 are flow diagrams depicting aspects of process flows inaccordance with the present invention.

FIG. 10 is a perspective view of a semiconductor workpiece thinnedaccording to a process of the present invention.

FIG. 11 is a cross-sectional view of the thinned semiconductor workpieceshown in FIG. 10.

DETAILED DESCRIPTION

With reference to FIGS. 1A-1E, there is shown a chuck 10 for supportinga semiconductor workpiece 50 during processing in accordance with oneembodiment of the present invention. The chuck 10 is comprised of asupporting body 12, a retainer 14 and a sealing members 16, 24. Theretainer 14 has two grooves or recesses 18. The sealing members 16, 24are housed in the annular grooves 18, respectively. The retainer 14 ispreferably in the form of a ring and is removeably attached to thesupporting body 12. In use, the workpiece 50, which has a device side51, a bevel (i.e., peripheral edge) 52 and a back side 53, is placedonto a supporting surface 18 of the supporting body 12 of chuck 50,device side 51 down. The retainer 14 is then attached to the outerperiphery of the supporting body 12. As shown specifically in FIG. 1C,when the retainer 14 is engaged to the supporting body 12, the retainer14 wraps around the outer end of the supporting body 12 and covers aperipheral portion of the back side 53 of the workpiece 50, securing theworkpiece 50 in the chuck 10.

When engaged, preferably the retainer 14 covers only a small peripheralportion of the back side 53 of the workpiece 50, leaving a majority ofthe back side 53 of the workpiece 50 exposed. In a preferred embodiment,the back side 53 surface area covered by the retainer 14 extendsinwardly from the bevel 52 for about a distance of approximately 1-10mm, more preferably between about 1-5 mm, and especially between about2-4 mm. Preferably, at least 95% (or even 97% or 99%) of the back side53 surface area of the workpiece 50 is left exposed. The exposed portionof the back side 53 of the workpiece 50 is then subjected to a processfluid and thinned to a desired thickness. As a result of covering theperipheral portion of the back side 53 of the workpiece 50, duringthinning, process fluid cannot interact with the periphery of the backside 53 of the workpiece 50. Accordingly, the periphery of the back side53 of the workpiece 50 remains in substantially its same pre-thinningform, configuration and thickness. For purposes of this invention, thesemiconductor material remaining at the periphery of the wokpiece 50after thinning is referred to as a rim. It is the rim that impartsstrength to the thinned workpiece 50 and permits automated handlingequipment to handle the thinned semiconductor workpieces 50 processedaccording to the present invention.

Turning to FIGS. 1D and 1E, in order to facilitate attachment of theretainer 14 to the supporting body 12, the retainer 14 has an engagementmember 20 that cooperates with a recess 22 formed in the supporting body12. In this manner, a simple mechanical snap connection between theretainer 14 and the supporting body 12 is achieved. Although not shownin FIGS. 1A-1D, the present invention includes a configuration where theengagement member 20 extends from the supporting body 12 and cooperateswith a recess 22 formed in the retainer 14 to removeably connect theretainer 14 and supporting body 12. In either configuration, preferablythe engagement member 20 and the recess 22 are positioned between thefirst and second sealing member 16, 24.

With reference to FIG. 1C, the retainer 14 has an outer peripheral end30 with an angled surface 32. When the retainer 14 is attached to thesupporting body 12, the angled surface 32 of the outer peripheral end 30of the retainer 14 mates with an angled surface 34 at an outerperipheral end of the supporting body 12 to form a notch 36. The notch36 accepts a tool (not shown) and facilitates removal of the retainer 14from the supporting body 12.

Turning now to FIG. 1E, the supporting body 12 has a lip or step 26formed circumferentially therein. The lip 26 acts to register or guidethe workpiece 50 as it is loaded into the chuck 10. When properlyaligned, the workpiece 50 will rest entirely on the supporting surface28 of the supporting body 12. While the chuck 10 can be any shape (e.g.,square, rectangular, circular, etc), as shown in FIGS. 1A-1E, in apreferred embodiment the chuck is disk-shaped and will have a diameterslightly larger than the diameter of the workpiece 50 to be processed.

With reference now to FIGS. 2A-2B, there is shown an alternativeembodiment of a chuck 10 according to the present invention. Like thechuck 10 shown in FIGS. 1A-1E, the chuck 10 includes a supporting body12 and a retainer 14. The retainer 14 has first and second sealingmembers 16, 24 disposed within annular grooves 18, 38. The mechanicalattaching mechanism in the embodiment illustrated in FIGS. 2A-2B,however, is slightly different than the mechanism shown in FIGS. 1A-1E.An engagement member 20 extends from the outer periphery of thesupporting body 12. The retainer 14, in turn, has a recess 22 thatcooperates with the engagement member 20 of the supporting body 12 toprovide a simple snap engagement that attaches the retainer 14 to thesupporting body 12. An upper portion of the retainer 14, includingsealing member 16, covers the exclusion zone of the back side 53 of theworkpiece 50 in the engaged position. In this preferred embodiment, theretainer 14 has a plurality of rinse holes 40 for allowing processingfluid to escape from cavities formed in the chuck 10. A lower portion 42of the retainer 14 which creates the mechanical snap connection with theengaging member 20 forms an annular recess 44 with a mating lowerportion 46 of the supporting body 12. A tool (not shown) can be insertedinto the annular recess 44 so that the retainer 14 can be simply poppedoff the chuck 10 supporting body 12 after processing is completed.

In the embodiments having two sealing members 16, 24 (as disclosed inFIGS. 1A-1E and 2A-2B), sealing member 16 creates a flexible interfaceand seal between the workpiece 50 and the retainer 14 to prevent processfluid from accessing the device side 51 and bevel 52 of the workpiece50. This flexible interface also relieves some of the stress that isexerted on the workpiece 50 during assembly and disassembly of the chuck10. Sealing member 24 creates a flexible interface between the retainer14 and the supporting body 12 and also helps relieve some of the stressthat is exerted on the workpiece 50 during assembly and disassembly ofthe chuck 10.

With reference now to FIGS. 3A-3B through 7A-7B, there is shown variouschuck 10 designs having only a single sealing member 16. Specifically,FIGS. 3A-3B illustrate a chuck 10 having a retainer 14, supporting body12 and a engagement mechanism similar to the engagement mechanism shownin FIGS. 2A-2B and described above. The retainer 14, however, has only asingle annular groove 18 which is adapted to house sealing member 16. Inthis embodiment, the annular groove 18 is V-shaped and receives asquare-shaped compressible sealing member 16. Preferably thesquare-shaped sealing member 16 has semi-circular extensions projectingfrom each corner to ensure an adequate fit in groove 18.

FIGS. 4A-4B and 5A-5B show chucks 10 having an engagement ring 48attached circumferentially to the bottom outer periphery of thesupporting body 12. The engagement ring 48 extends radially outwardlyfrom the supporting body 12, creating a stepped-relationship between thesupporting body 12 and engagement ring 48, and forming engagement member20. The retainer 14 has a lower portion 42 with a U-shaped recess 22formed therein. The U-shaped recess 22 receives the engagement member20. The lower portion 42 of the retainer 14 has an extension 49 thatwraps around the engagement member 20 to form a mechanical snapconnection between the retainer 14 and the engagement ring 46 of thesupporting body 12. In FIGS. 4A-4B, the retainer 14 has a two-stepannular groove 18 which receives a sealing member 16 having a top partwith one width for insertion into one-step of the annular groove 18, anda bottom part with a second width for insertion into the second step ofthe annular groove 18. In FIGS. 5A-5B, the retainer 14 has a singleV-shaped annular groove 18 for housing the sealing member 16, which inthis embodiment is a compressible O-ring.

FIGS. 6A-6B illustrate another preferred embodiment of a chuck 10according to the present invention. In this embodiment, the lowerportion 42 of the retainer 14 has an inner side wall 60 with a convexprotrusion 62 extending outwardly therefrom. The supporting body 12 hasan end wall 64 with a concave recess 66 for accepting the convexprotrusion 62 of the inner side wall 60 of the lower portion 42 of theretainer 14. In this manner, the retainer 14 engages the supporting body12 and secures the workpiece 50 on the supporting surface 28 of thechuck 10.

In the embodiments having only a single sealing member 16 (as disclosedin FIGS. 3A-3B through 6A-6B), sealing member 16 creates a flexibleinterface between the workpiece 50 and the supporting body 12 to preventprocess fluid from interacting with the device side 51 and bevel 52 ofthe workpiece 50, and to relieve stress exerted on the workpiece duringthe assembly/disassembly process.

Turning now to FIGS. 7A-7B, there is shown a preferred embodiment of achuck 10, which combines the retainer 14 and sealing member 16 of theprior embodiments. In this embodiment, retainer 14 is asingle-component, compressible annular ring with an annular groove 18running circumferentially through the middle of the retainer 14. Thesupporting body 12 has an outer end 13, which is inserted into theannular groove 18 in the retainer 14. The retainer 14 remains engaged tothe supporting body 12 as a result of a compression force exerted by theretainer 14 onto the supporting body 12 and the workpiece 50. In theattached position, an outer peripheral portion of the workpiece 50(e.g., the exclusion zone) is also positioned within the annular groove18. In this preferred embodiment, retainer 14 creates a seal with theback side 53 of the workpiece 50, preventing process fluid fromaccessing the bevel 52 and device side 51 of the workpiece 50 duringprocessing.

Suitable materials for use in the chuck 10 embodiments according to thepresent invention will now be discussed. Generally, the chuck 10 can bemade from a number of different polymer materials that are stable andhighly chemically resistant. Preferably the supporting body 12 comprisespolytetrafluoroethylene and the retainer 14 preferably comprises afluoropolymer such as polyvinylidene fluoride sold by Atofina Chemicalsunder the KYNAR tradename. In the embodiment illustrated in FIGS. 7A-7B,the retainer 14 is preferably formed from a material having a Durometerhardness less than that of a fluoropolymer, but greater than theelastomeric materials discussed below with respect to the sealingmember. That is, a material compressible enough to form a seal with theworkpiece 50, but stiff enough to provide structure to the retainer 14for receiving the supporting body 12. In any embodiment of the presentinvention, in order to enhance the attachability of the retainer 14 tothe supporting body 12, it is preferred that the supporting body 12 iscomprised of a material having a Durometer hardness greater than theDurometer hardness of the material from which the retainer 14 is formed.

As illustrated in FIGS. 1A-1E, 2A-2B, 5A-5B and 6A-6B, the sealingmembers 16, 24 are preferably shaped like an “O-ring,” but it iscontemplated that other shapes can be used as well (e.g., as shown inFIGS. 3A-3B and 4A-4B). The sealing members 16, 24 are preferably formedfrom a compressible material having a Durometer hardness equal to orgreater than 50. Specific examples of suitable elastomeric materialsinclude: a perfluoroelastomer sold by DuPont under the tradename Kalrez;a perfluoroelastomer sold by Greene, Tweed & Co. under the tradenameChemraz; fluoruelastomers sold by DuPont under the tradename Viton; andhydrocarbon elastomers sold under the tradename EPDM.

Turning now to the workpiece thinning processes according to the presentinvention, FIG. 8 illustrates one embodiment of a process that may beimplemented when the chuck 10 and workpiece 50, described above, areused to thin the back side 53 of the workpiece 50. At step 200, aworkpiece 50 is provided having a device side 51, a bevel 52 and a backside 53. The back side 53 of the workpiece 50 will have a given surfacearea depending on its dimensions. Also, the workpiece 50 has a giventhickness.

At step 210, the workpiece 50 is placed onto the supporting surface 28of chuck 10 with the device side 51 immediately adjacent to thesupporting body 12 of the chuck 10. The retainer 14 is attached to thesupporting body 12 so that a peripheral portion (e.g., the exclusionzone of the workpiece 50) of the back side 53 of the workpiece 50 iscovered. In step 210, the workpiece 50 is secured to the chuck 10. As aresult of the chuck 10 configuration, upon attaching the retainer 14 tothe supporting body 12, in step 220 a majority (and preferably at least95%, more preferably at least 97% and especially at least 99%) of theback side 53 surface area is exposed, while a small peripheral portionof the back side 53 of the workpiece 50 is covered.

The workpiece 50 is then thinned to a desired thickness at step 230 byapplying a process fluid to the exposed back side 53 of the workpiece50. Due to the overlapping configuration of the retainer 14, by thinningthe exposed back side 53 of the workpiece, at step 240, a rim and a mainbody is formed in the workpiece 50. The rim is formed at the outerperiphery of the workpiece 50 and has a thickness, RT and the main bodyof the workpiece 50 has a thickness, MBT. In the preferred embodiment ofFIG. 8, the MBT is less than approximately 50% of the RT. A desired MBTis preferably less than approximately 40% of the RT; more preferablyless than approximately 30% of the RT; especially less thanapproximately 20% of the RT; and even less than approximately 10% of theRT. It should be understood that after thinning the workpiece 50, the RTshould be substantially the same as the workpiece 50 thickness prior tothe thinning process. Thus, for conventional 200 mm and 300 mmworkpieces, the RT after thinning will be about 725 microns. And the RTof a conventional 150 mm workpiece after thinning will be about 650microns.

It is within the scope of the present invention, however, to process aworkpiece 50, which has previously been thinned by some other method,e.g., mechanical grinding. Thus, a workpiece 50 having a thickness ofanywhere from 150-725 microns can be thinned according to the presentinvention to create a workpiece 50 with a rim having a RT in a range ofsubstantially the same thickness as the workpiece 50 (i.e., about150-725 microns, even about 600-725, or even about 300-725) and a mainbody having a MBT in a range of about 25-300 microns, preferably in arange of about 100-125 microns, more preferably in a range of about50-100 microns, especially in a range of about 25-50 microns.

Turning now to FIG. 9, there is shown another embodiment of a processthat may be implemented when the chuck 10, described above, is used tothin a workpiece 50. At step 300, a workpiece 50 having a thickness,WPT, is provided. The workpiece 50 has a device side 51, a bevel 52 anda back side 53. The workpiece 50 is placed onto the chuck 10 with thedevice side 51 immediately adjacent to the supporting body 12 of thechuck 10 at step 310. At step 320, the retainer 14 is attached to thesupporting body 12 so that a peripheral portion of the back side 53 ofthe workpiece 50 is covered. In this step, the workpiece 50 is securedto the chuck 10. As a result of the chuck 10 configuration, when theretainer 14 is attached to the supporting body 12, with the exception ofthe covered exclusion zone, substantially all of the back side 53 of theworkpiece 50 is exposed.

Still referring to FIG. 9, at step 330 the chuck 10 and workpiece 50 areplaced into a process chamber. The processs chamber may be manual orautomated and is preferably within a spray acid tool platform like thoseavailable from Semitool, Inc., of Kalispell, Mont. Once inside theprocess chamber, a process fluid is applied to the exposed back side 53of the workpiece 50 at step 340. The thinning process of step 340preferably comprises a conventional wet chemical etch process or apolishing process. In either process, the process fluid preferablyconsists of one, or a combination of: deionized water, hydrogenperoxide, ozone, potassium hydroxide, sodium hydroxide, hydrofluoricacid, nitric acid, sulfuric acid, acidic acid and phosphoric acid. Anumber of other acidic and basic solutions may also be used, dependingon the particular surface to be treated and the material that is to beremoved.

The process fluid can be applied to the workpiece 50 in any conventionalmanner. In one preferred embodiment, however, the process fluid issprayed through a nozzle or a plurality of nozzles onto the back side 53of the workpiece 50. In another preferred embodiment, the chuck 10 andworkpiece 50 are immersed into a volume of process fluid, orsequentially into a plurality of volumes of the same process fluid (atdifferent concentrations or temperatures) or different process fluids.

Depending on the composition of the material to be removed and theamount of material to be removed (i.e., the desired end thickness of theworkpiece), the process fluid will have a desired concentration, atemperature and a flow rate. By monitoring and maintaining these processfluid variables, the process fluid can be applied to the exposed backside 53 of the workpiece 50 at a first etch rate, and then subsequentlyat a second etch rate. Preferably, the first etch rate is greater thanthe second etch rate. That is, semiconductor material is etched awayquickly at first, and then more slowly as the thickness of the workpiece50 approaches the desired thickness.

Referring to step 350 of FIG. 9, the thinning process forms a rim 70 anda main body 72 in the workpiece 50. The thinning process is carried outuntil the main body 72 reaches a desired thickness, MBT. Preferably, theMBT is less than 50% of the WPT, more preferably less than 40% of theWPT, even more preferred less than 30% of the WPT, especially less than20% of the WPT and especially preferred less than 10% of the WPT. It ispreferable to measure the thickness of the main body 72 of thesemiconductor workpiece 50 throughout the thinning process. This can beaccomplished by employing conventional infrared monitoring technology inthe process chamber, or by any other known measuring technique such as acapacitive measurement technique. If need be, the process fluidvariables described above can be adjusted based on the continuedmonitoring of the workpiece thickness.

At step 360, the thinned workpiece 50 is rinsed and dried. For example,the workpiece may be sprayed with a flow of deionized water, nitrogen orphosphoric acid during the rinsing step and may then be subject to anyone or more known drying techniques thereafter. Finally, the workpiece50 is then removed from the chuck (step 370) and the thinned workpiece50 is diced into a plurality of dies (step 380).

Thinning of semiconductor workpieces 50 can be carried out on a singleworkpiece 50, or on a plurality of workpieces 50 simultaneously,according to the present invention. When thinning a plurality ofworkpieces 50, it is desirable to place each workpiece 50 into acorresponding chuck 10 and then place the plurality of chucks 10 andworkpieces 50 into a carrier such as the carriers disclosed inco-pending U.S. patent applications Ser. Nos. 10/200,074 and 10/200,075,the disclosures of which are incorporated herein by reference. Once theplurality of workpieces 50 (and associated chucks 10) are placed in thecarrier, the carrier is loaded into a process vessel and a process fluidis applied to the exposed back sides 53 of the plurality of workpieces50. In order to ensure an adequate application of the processs fluid tothe workpieces 50, it is preferable to rotate the chucks 10 or thecarrier, or both, within the process vessel during processing. Theprocess vessel can be a stand alone tool, or one of a plurality ofworkstations making up a larger, workpiece 50 processing system.

With reference now to FIGS. 10-11, the resulting thinned semiconductorworkpiece 50 processed according to the process of the present inventionwill be described. As described above, the thinned workpiece 50 iscomprised of a rim 70 and a main body 72. The rim 70 is formed at theperiphery of the workpiece 50 and is integral with the main body 72.Generally, when processing standard semiconductor workpieces 50, theprocessed workpiece 50 will have a main body 72 with a thickness lessthan 125 microns and a rim 70 with a thickness in a range ofapproximately 600 to 725 microns. In a preferred embodiment, however,the main body 72 thickness will be less than 100 microns, morepreferably less than 50 microns, and especially less than 25 microns. Asmentioned, the rim 70 is formed at the exclusion zone of the workpiece50 and will have a width (shown as w in FIG. 10) in a range of 1-10 mm,preferably a range of 1-5 mm and especially in a range of 1-2 mm. Themain body 72 and rim 70 are formed from substantially the same materialas the pre-thinned workpiece 50. Most preferably the main body 72 andrim 70 are comprised of silicon.

As also mentioned above, it is contemplated that workpieces 50 that havepreviously been thinned by another process can be thinned according tothe present invention. In these instances, the initial thickness of aworkpiece 50 to be thinned according to the present invention may be 200microns or less. In such case, a workpiece 50 thinned according to thepresent invention will have a main body 72 thickness less than about 50%of the rim 70 thickness, preferably less than about 40% of the rim 70thickness, more preferably less than 30% of the rim 70 thickness,preferentially less than 20% of the rim 70 thickness, even less than 10%of the rim 70 thickness and especially less than 5% of the rim 70thickness. It is also contemplated that the present invention can beused to thin workpieces 50 of varying sizes. Accordingly, the rim 70will preferably comprise less than approximately 5% of the back side 53surface area (BSSA) of the workpiece 50, more preferably less than 3% ofthe BSSA, and even less than 1% of the BSSA.

Numerous modifications may be made to the foregoing invention withoutdeparting from the basic teachings thereof. Although the presentinvention has been described in substantial detail with reference to oneor more specific embodiments, those of skill in the art will recognizethat changes may be made thereto without departing from the scope andspirit of the invention.

1. A process for thinning a semiconductor workpiece having a device sideand a back side, the back side having a back side surface area, BSSA,comprising: placing the semiconductor workpiece into a chuck, the deviceside of the workpiece being free from a protective tape or polymer;covering a peripheral portion of the back side of the workpiece leavingat least 95% of the BSSA is exposed; and thinning the exposed back sideof the workpiece to create a rim having a thickness, RT, and a main bodyhaving a thickness less than approximately 50% of the RT the rimextending outwardly from the back side of the workpiece but not from thedevice side of the workpiece.
 2. The process of claim 1, wherein themain body has a thickness less than approximately 40% of the RT.
 3. Theprocess of claim 1, wherein the main body has a thickness less thanapproximately 30% of the RT.
 4. The process of claim 1, wherein the mainbody has a thickness less than approximately 20% of the RT.
 5. Theprocess of claim 1, wherein the main body has a thickness less thanapproximately 10% of the RT.
 6. The process of claim 1, wherein at least97% of the BSSA is exposed.
 7. The process of claim 1, wherein at least99% of the BSSA is exposed.
 8. The process of claim 1, wherein the rimis formed at the periphery of the workpiece.
 9. The process of claim 1,wherein RT is in a range of 200 to 725 microns.
 10. The process of claim9, wherein the main body has a thickness in a range of about 100 to 120microns.
 11. The process of claim 9, wherein the main body has athickness in a range of about 50 to 100 microns.
 12. The process ofclaim 9, wherein the main body has a thickness in a range of about 25 to50 microns.
 13. The process of claim 1, wherein the main body has athickness in a range of about 100 to 120 microns.
 14. The process ofclaim 1, wherein the main body portion has a thickness in a range ofabout 50 to 100 microns.
 15. The process of claim 1, wherein the mainbody portion has a thickness in a range of about 25 to 50 microns.
 16. Aprocess for thinning a semiconductor workpiece having a workpiecethickness, WPT, the process comprising: providing the semiconductorworkpiece with a back side and a device side both being free from aprotective film or tape; placing the semiconductor workpiece onto achuck body so that the back side of the workpiece is exposed; attachinga retainer to the chuck body so that the workpiece is secured to thechuck and a peripheral portion of the back side of the workpiece iscovered by the retainer; and thinning the exposed portion of the backside of the workpiece to create a rim and a main body portion, the mainbody portion having a thickness, MBT, less than 50% of the WPT and therim extending outwardly from the back side of the workpiece but not fromthe device said of the workpiece.
 17. The process of claim 16, whereinthe step of thinning the exposed portion of the back side of theworkpiece comprises chemically etching semiconductor material away fromthe exposed portion of the back side of the workpiece.
 18. The processof claim 17, wherein the step of thinning the exposed portion of theback side of the workpiece further comprises the step of polishing theexposed portion of the back side of the workpiece.
 19. A process forthinning a semiconductor workpiece having a workpiece thickness, WPT,and a device side and a back side, the process comprising: placing thesemiconductor workpiece in a chuck without applying a protective layerto the workpiece the chuck being adapted to surround a peripheralportion of the back side of the workpiece and the device side of theworkpiece so that a main body portion of the back side of the workpieceis exposed; placing the chuck and workpiece into a process vessel; andapplying a process fluid to the exposed main body portion of the backside of the workpiece to thin the main body portion to less than 50% ofthe WPT and create a rim that extends outwardly from the back side ofthe workpiece.
 20. The process of claim 19, wherein the step of applyinga process fluid to the exposed main body portion comprises spraying theprocess fluid through a nozzle onto the main body portion of the backside of the workpiece.
 21. The process of claim 19, wherein the step ofapplying a process fluid to the exposed main body portion comprisesimmersing the exposed main body portion into a volume of the processfluid.
 22. The process of claim 19, wherein the process fluid is aprocess fluid selected from the group consisting of water, hydrogenperoxide, ozone, potassium hydroxide, sodium hydroxide, hydrofluoricacid, nitric acid, sulfuric acid, acidic acid and phosphoric acid. 23.The process of claim 19 further comprising a step of rinsing the mainbody portion of the workpiece after it is thinned.
 24. The process ofclaim 23, wherein the rinsing step comprises applying phosphoric acid tothe main body portion of the workpiece after it is thinned.
 25. Theprocess of claim 23 further comprising a step of drying the thinnedworkpiece.
 26. The process of claim 19, wherein the process fluid isapplied to the exposed main body portion at a first etch rate and thensubsequently applied at a second etch rate.
 27. The process of claim 26,wherein the first etch rate is greater than the second etch rate. 28.The process of claim 19 further comprising the step of measuring thethickness of the main body portion of the workpiece.
 29. The process ofclaim 19, wherein the process fluid has a flow rate, a concentration anda temperature and the process further comprises a step of monitoring atleast one of the flow rate, concentration and temperature of the processfluid.
 30. A process for thinning a semiconductor workpiece, the processcomprising: placing the semiconductor workpiece onto a chuck, thesemiconductor workpiece having a device side and a back side free from aprotective film, layer and tape; attaching a retainer to the chuck tosecure the work piece to the chuck and surround a peripheral portion ofthe back side of the workpiece so that a main body portion of the backside of the workpiece is exposed; placing the chuck in a carrier;loading the carrier into a process vessel; rotating the chuck in theprocess vessel; and applying a process fluid to the exposed main bodyportion of the back side of the workpiece as the chuck rotates to thinthe main body portion of the back side of the workpiece to a thicknessand create a rim having a thickness greater than the main body portionthickness.
 31. A process for thinning a semiconductor workpiece, theprocess comprising the steps of: providing a semiconductor workpiecehaving a back side and a device side, the device side and the back sidebeing free from a protective film, tape and layer; placing thesemiconductor workpiece in a chuck configured to protect the device sideof the semiconductor workpiece; and thinning the back side of thesemiconductor workpiece to create a rim having a thickness, RT, and amain body having a thickness, MBT, wherein MBT is less thanapproximately 50% of the RT and the rim extends outwardly from the backside of the semiconductor workpiece but not from the device side of thesemiconductor workpiece.
 32. The process of claim 31, wherein the stepof thinning comprises chemically etching semiconductor material awayfrom the back side of the semiconductor workpiece.
 33. The process ofclaim 31, wherein the step of thinning comprises grinding the back sideof the semiconductor workpiece.
 34. The process of claim 31, wherein thestep of thinning comprises: grinding the back side of the semiconductorworkpiece; and etching the ground back side of the semiconductorworkpiece with a process fluid.
 35. The process of claim 31, wherein theMBT is less than 125 microns.
 36. The process of claim 31, wherein theMBT is less than 100 microns.
 37. The process of claim 31, wherein theMBT is less than 50 microns.
 38. The process of claim 31, wherein theMBT is less than 25 microns.
 39. The process of claim 31, wherein thestep of protecting the back side of the semiconductor workpiececomprises placing the semiconductor workpiece into a chuck.
 40. Theprocess of claim 39, wherein the chuck is adapted to cover a peripheralportion of the back side of the workpiece leaving at least 95% of asurface area of the back side exposed.
 41. A process for thinning asemiconductor workpiece, the process comprising the steps of: providinga semiconductor workpiece having a back side and a device side, thesemiconductor workpiece having a workpiece thickness WPT; protecting thedevice side of the semiconductor workpiece without applying a protectivelayer to the device side of the semiconductor workpiece; thinning theback side of the semiconductor workpiece to create a rim having a rimthickness, RT, and a main body having a mainbody thickness, MBT, whereinRT is approximately equal to WPT, and MBT is less than approximately 20%of RT; removing the protection from the device side of the semiconductorworkpiece; and dicing the workpiece into a plurality of dies.
 42. Theprocess of claim 41, wherein WPT is in a range of 150-725 microns. 43.The process of claim 42, wherein MBT is in a range of 30-145 microns.